Last month, the Nobel Prize for physics was awarded to three scientists who discovered that, since the Big Bang, the universe has been expanding at an accelerating rate. Before the discovery, scientists assumed that gravity slowed down the expansion of the universe. But the data collected by one team led by astrophysicist Saul Perlmutter and another team led by physicist Brian Schmidt indicated otherwise.

"When we started getting results that showed that it was not slowing ... [that] in fact it wasn't slowing at all — it was speeding up — it was a pretty big shock," says Perlmutter, an astrophysicist at the Lawrence Berkeley National Laboratory. "At the time, when you first get those results, it doesn't worry you too much ... because you know you haven't finished doing the calibration. The more we did the calibration, the more the results didn't go away."

Perlmutter, Schmidt and Adam Riess, who played a crucial role on Schmidt's team, shared the 2011 Nobel Prize in physics for their 1998 discovery, which involved studying distant exploding stars called Type Ia supernovae. By looking at the brightness and color of light coming from the supernovae, the scientists were able to figure out that the universe has expanded faster in the past 5 billion years instead of slowing down, as it was before that. Their findings — from two independent observations — both shocked and fascinated the scientific community.

"It would be a little like throwing an apple up in the air and you would expect that it would be pulled back down due to gravity," Perlmutter tells Fresh Air's Terry Gross. "What we were seeing was a little bit like throwing the apple up in the air and seeing it blast off into space."

To see the supernovae, Perlmutter's team had to reserve time at some of the biggest and most advanced telescopes in the world. But there were problems with that, he says. Supernovae are notoriously tricky — although they're super bright, they give no advance warning when they're about to explode (so that scientists can measure their brightness) and they only stay at their peak brightness for a short time before they start to fade.

And if the sky is cloudy? Tough luck.

"You have to apply for [the biggest telescopes] months in advance, and you might get one or two nights — and it makes a terrible proposal to say, 'I'd like to use the Keck telescope on the night of March 3 because sometime in the next few hundred years a supernova might explode,'" jokes Perlmutter. "So when we started the project, it seemed a little bit quixotic. We had to figure out ways that would otherwise be an awkward project into something that could be practical and reliable."

Perlmutter's team designed advanced equipment and a search strategy so that a lot of data could be captured and analyzed after their time at the telescopes. "Once we figured out how to do that, we were able to guarantee batches of supernova data on a certain date," he says.

Is The Universe Empty — Or Filled With Dark Energy?

The results of Perlmutter, Riess and Schmidt's research may suggest that the empty space in the universe isn't really empty — that it might be filled with what scientists called dark energy. The dark energy, spread throughout the universe, is thought to be associated with all empty space and is somehow working against gravity to push the universe apart faster and faster.

"If that is the explanation, then most of the universe is actually made up of this dark energy, which we've never previously studied," says Perlmutter. "It was not part of our accounting of all of our forces and particles in the universe up until now, and that's amazing. We have a remarkably complete picture in many ways — and it could be that we're not accounting for something that's almost three-quarters of the entire universe."

If you're puzzled by what dark energy is, you're in good company, says Perlmutter.

"At this point, I think there's been a paper averaging almost every day for the past 12 years with theorists of physics trying out different ideas for what could be the explanation," he says. "If you ask almost any of them, 'Do you stand behind your theory? Is this the answer?' I think almost everyone would say, 'No, no, no. I'm just trying to expand the range of possibilities.' We really don't know what's going on."

Another possibility? That Einstein's theory of general relativity needs to be modified for something on the scale of the entire universe.

"That would be remarkable, because Einstein's theory is so successful down to many digits of precision," says Perlmutter. "So the ideas that you can get another theory that you'd slightly modify and is just as good would be amazing."

Rethinking What They Know

Though scientists don't yet know the reason why the expansion of the universe is speeding up, they are excited by the possibility to rethink what they do know, says Perlmutter.

"From our point of view, the most exciting thing would be if we discovered something really fundamental in our understanding was just off a bit — and that now we have a chance to revisit it," he says. "That would be our favorite thing, if we could take a whole new crack at the problem — and a new way of understanding it. In physics, it seems like whenever we get a completely new understanding ... it somehow subsumes the previous understandings and it ... adds an extra level of sophistication."

Perlmutter, a professor at the University of California, Berkeley, teaches a popular class on the physics of music. As part of his Nobel Prize winnings, he receives a cash prize from the Nobel committee — and a free parking spot from Berkeley.

"They already put up the parking spot sign, so it's now in a row of spots for Nobel laureates," he says. "And I will say that growing up as a kid in an urban environment and having lived in cities all my life, the one achievement that everyone can look forward to is getting the perfect parking spot."

We're going to think big today - really big, infinity big - the universe. My guest, astrophysicist Saul Perlmutter, was awarded the Nobel Prize in Physics last month. He shares it with two other physicists from a competing team which discovered the same thing his team did.

Perlmutter's team found that the universe was expanding at an accelerating rate, which is pretty much the opposite of what he'd set out to prove. The fact that the rate of expansion is accelerating, not slowing, has huge implications for what we think of as the empty space in the universe and its ability to somehow work against gravity. To conduct its work, Perlmutter's team used the largest telescopes in the world to track supernova.

Perlmutter heads the Supernova Cosmology project at the Lawrence Berkeley National Laboratory in the University of California at Berkeley. He's a professor of physics at the university.

Saul Perlmutter, congratulations on the Nobel and welcome to FRESH AIR.

PROFESSOR SAUL PERLMUTTER: Thank you.

GROSS: So when you started your research, you expected to find that the universe was still expanding, but the rate at which it was expanding was slowing down. What you found was the opposite, that the rate at which the universe is expanding is actually speeding up.

How surprised were you when you found out that the results were contradicting your expectations?

PERLMUTTER: When we began the project, it was - it seemed like a very exciting project and very straightforward, that we would just measure how much the universe was slowing down. Because all the gravity of all the stuff in the universe would tend to attract each other, and the universe would tend to slow in its expansion.

So when we started getting results that showed that it was not slowing, and certainly not slowing enough to come to a halt - in fact, it wasn't slowing at all, it was speeding up - it was really a pretty big shock.

At the time, when you first get those results, it doesn't worry you too much for a very interesting reason. Which is that you're putting together a big chain of analysis, with lots of little steps that you have to finish and calibrate. And you put it all together and you look at the very first results and they look a little funny, but you don't take it very seriously because you know that you haven't yet finished doing the calibration.

The more we did the calibration, the more the results didn't go away. And that was when things started getting interesting.

GROSS: So OK. So you found the universe is expanding at an increasingly fast rate. Why is that so remarkable?

PERLMUTTER: Well, we all assumed that gravity was going to be the main player in the expansion of the universe and that all the stuff in the universe would tend to attract each other and that would slow this expansion down. It would be a little bit like throwing an apple up in the air and you expect that it will get pulled back down to Earth by gravity.

What we were seeing was a little bit like throwing the apple up in the air and it blasting off into space. And clearly there's something else going on here that was not part of our standard physics. And physics has been doing very well at predicting these kinds of things. Here we've suddenly found something that it was just getting wrong.

GROSS: So does this finding challenge the law of gravity?

PERLMUTTER: There are a couple of ways that people are trying out to explain what's going on. Why is it that the universe is expanding faster and faster? Some of them involve considering a new energy that could be spread throughout all of space. And we're calling it dark energy for the moment as a placeholder, just because we don't yet know what its properties are.

If that is the explanation, then most of the universe is actually made up of this dark energy that we've never previously studied.

It's also possible on that Einstein's Theory of General Relativity, which our fundamental theory of gravity, may need a little bit of a modification, a little bit of a tweak when you use it to describe things on the huge scale of the universe. That would be remarkable because Einstein's theory is so successful down to, you know, many digits of precision that it's - the odds that you can get another theory that you would slight modify, and it it's just as good, would be amazing.

GROSS: So you're one of the people who discovered that there might be a force, an energy that we never knew about before.

PERLMUTTER: That's right. So one of the explanations for what's going on is this energy that's spread throughout all of space, and this is saying that we have not really studied previously, it was not part of our accounting of all the forces and particles in the universe up till now, and that's amazing 'cause we've been - we have a remarkably complete picture in many ways. And yet it could be that we're not accounting for something that's almost three-quarters of the universe - its energy and mass is made up of this.

GROSS: So when you say it's three-quarters of the universe, is it the space between planets and galaxies?

PERLMUTTER: This dark energy, if that turns out to be the right explanation, is thought to be an energy that's associated with all of empty space. Any space at all in the universe would have some of this energy that's basically making space want to reproduce itself faster and faster, that's making, you know, our universe expand at an accelerated rate.

GROSS: So it's just kind of amazing to me...

(SOUNDBITE OF LAUGHTER)

GROSS: ...that there's this force out there that like no one ever knew about and you helped discover it. And I'm trying to kind of fathom like what it is. But why should I be able to do it? I mean I've seen dark energy described as the most important problem facing 21st century physics, so why I should understand it?

(SOUNDBITE OF LAUGHTER)

PERLMUTTER: Right. I've been saying to people that if you're puzzled by what dark energy is, you're in good company. That it's at this point, oh, I think there's been a paper almost - averaging almost every day for the past 12 years with theorists of physics trying out different ideas for what could be the explanation. And if you ask almost any of them, do you stand behind your theory, is this the answer, I think they would almost every one say that no, no, no, I'm just trying to expand the range of possibilities.

We really don't know what is going on. And in fact, if anything, the theorists start turning back to us the observation list, the experimental list, and saying, you've got to give us a little more of a clue of some of the properties of this phenomenon so that we can home in on some real - on a real likely answer.

GROSS: Is it possible that dark energy is a force that is in opposition to gravity?

PERLMUTTER: Dark energy, in our current picture, isn't exactly a force. So it's not, you know, like an anti-gravity per se. It - in its effect on how the universe expands, it happens to work in the opposite direction from gravity. But forces tend to operate between objects. You know, so two masses fill gravity with each other.

This dark energy, it doesn't really care about the objects. It's in some sense a property of space itself and space itself wants to reproduce faster and faster.

GROSS: So how does this relate to the Big Bang Theory of the creation of the universe?

PERLMUTTER: It's remarkable how much we've been able to figure out about the expansion of the universe, about the origin of the elements. And we, you know, we wrap it all up together in the term the Big Bang Theory. And - but of course it includes many things that now we think we understand how they came to look the way they do today.

This particular part of the story is one which it doesn't change the explanations for the things that we've already seen, but it puts a new twist on it. It allows there to be now an extra element of the picture that we have to also explain.

It may relate to the very first fraction of a second where the universe was thought to undergo a very rapid acceleration before it started slowing down, in the first half of its lifetime. And then now apparently, in the last half of its, you know, 14 billion years of history, it's been starting to speed up again. And some are asking is there any connection between those two periods in which it accelerated. But at the moment we don't know.

GROSS: So it doesn't challenge the Big Bang Theory. It just adds another question mark to it.

PERLMUTTER: Exactly. So at this point most of the elements of the Big Bang Theory seem to still hold very well. But the fact that you have a new wrinkle in the story always gives you a new chance to rethink, and people are busy rethinking. So we think that this could be a whole new element of our fundamental theories of particles and forces and it could be a whole new element of our theory of cosmology, how the universe formed and how and why it looks the way it does. But whatever we used to explain those, this new element has to work and preserve everything we've already understood so that we don't lose our theory of cosmology and our theory of physics while we try to understand this. It has to add to this in some sense.

GROSS: Let's hope.

(SOUNDBITE OF LAUGHTER)

GROSS: That it doesn't contradict everything we thought we knew. Do you worry about that?

PERLMUTTER: Well...

GROSS: All the things we know about physics are going to start to fall apart because of your discovery?

PERLMUTTER: There's a great New Yorker cartoon which have somebody watching the television and the newscasters is saying things like: Today scientists announced that everything we thought we knew about the world was wrongedy-wrong-wrong.

(SOUNDBITE OF LAUGHTER)

GROSS: And so do you worry about that?

PERLMUTTER: Well, I mean from our point of view the most fun thing, the most exciting thing would be if we discovered that something really fundamental in our understanding was just off, and that now we have a chance to revisit it. And for us, you know, for the scientists, for the physicists, you know, that would be our favorite thing - if we got a whole new crack at the problem and a new way of understanding it.

So far so much of what they understand fits so well together and dovetails so perfectly that it's hard to believe that everything just falls apart. In fact, in the history of physics it seems that whenever we get a completely new understanding, like Einstein's theory of relativity, it somehow subsumes the previous understanding like Newton's theory of gravity and it keeps all the explanations still good that you had before but now it adds an extra level of sophistication to the understanding.

GROSS: If you're just joining us, my guest is Saul Perlmutter and he shares this year's Nobel Prize in science for the discovery of the accelerating expansion of the universe, and he heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory and the University of California at Berkeley.

Let's take a break here, then we'll talk some more. This is FRESH AIR.

(SOUNDBITE OF MUSIC)

GROSS: If you're just joining us, my guest is Saul Perlmutter who shares this year's Nobel Prize in science for discovering that the universe is expanding at an accelerating rate, and this also postulates the existence of dark energy, which could help explain why the universe is expanding at an increasing - accelerating rate. He heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory in the University of California at Berkeley.

So to calculate that the universe is expanding at an accelerating rate, you had to figure out like how do you measure that? So you measured that by measuring the brightness of supernovas. So before we go any further...

(SOUNDBITE OF LAUGHTER)

GROSS: ...could you tell us what supernova are?

PERLMUTTER: At the end of a star's life, when it's used up most of its fuel, it can die away as a quiet ember and never bother anybody. This would be a star, you know, around the mass of our sun would do that. But many such stars will have other stars orbiting around them relatively nearby. And those stars can add little bits of mass and little bits mass to this dying ember until there's just a critical mass and at that point there's away from a nuclear explosion. So there's at least some kinds of supernova that appear to be triggered explosions and they seem to reach the same brightness and then fade away every time. So they bright and a couple of weeks and then they fade away in a few months. But you catch them just before they peak and you measure how bright they were at peak, you'll pretty much know that they're all about the same.

GROSS: OK. You are leaving out I think the fact that these nuclear-type explosions of the stars happened like five billion years ago.

PERLMUTTER: Yes. So that explosion, you know, occurs, you know, in some distant star, in some distant galaxy and then there's a - this little, you know, fireworks of light. But it takes then long time for that light to travel across the universe from their galaxy to our galaxy and to find us at our telescope and for us to see that little pulse of light that arrives. And, you know, we have examples now of supernova where we see a little bit of history, a little bit of what happened out that distant galaxy when that of pulse of light arrives to us, oh, you know, two billion years later, five billion years later. And so we now know about a month of history from five billion - in fact, our furthest one is almost 10 billion years back.

GROSS: So without getting too mathematical on us...

(SOUNDBITE OF LAUGHTER)

GROSS: ...like how does observing the brightness of supernova that exploded five billion years ago help you determine the rate at which the universe is accelerating?

PERLMUTTER: The fun thing about this particular measurement is that it's one of the most direct simple measurements that I know about that gets at something really fundamental. And so it's kind of fun just to tell the story. We use the fact that these particular kinds of supernova that we can recognize, they're called type 1-As, all reached about the same brightness by measuring how bright they appear to us. So here on Earth we just measure how bright it appears and since you know that they were all intrinsically the same brightness now you know all the relative distances between these supernovas. So the brighter ones are closer and you know how much closer than the fainter ones which are further.

The one other element to that story is that if you know how far away something is, you also know how long ago the light left that object. So the supernova exploded maybe five billion years ago and the light's been traveling to us, but we know the speed of light. So we know by just the brightness of the supernova how far away it is and hence, how far back in time that particular explosion occurred.

If you find a series of supernova, you know, one that's, you know, this brightness, one that's fainter by that amount, the other ones even more faint, you now have a few marker points in history. You have one let's say that was tells you about what the universe looked like two billion years ago, one that tells you about what the universe looked like four billion years ago, and maybe one that tells you how much the universe looked like seven billion years ago, and that's the beginning of our measurement.

GROSS: I guess I still don't understand on how that tells you the rate of acceleration.

PERLMUTTER: Ah, so that's not the whole measurement.

(SOUNDBITE OF LAUGHTER)

GROSS: OK.

PERLMUTTER: OK. So now we have a marker at several different times in history. What we want to know is how much has the universe has expanded since each of those times and that will tell us the history of the expansion. And what we do is just look at the colors of the light that comes from the supernova. If you looked at the supernova, you know, up close, and then if you didn't die, it would look blue mostly and that's a short wavelength of light. And as the universe expands everything that's in it that's not nailed down expands just with the universe and that includes the very photons of light that are traveling to us from the distant supernova. So they get stretched out just like the whole universe gets stretched out and what used to look blue and with a short wavelength, by the time it reaches us it looks a lot redder with a longer wavelength. And we can just read off how much the universe has stretched by how much this wavelength has stretched and how red the light has gotten.

GROSS: OK. I'm going to pretend like I can really comprehend that.

(SOUNDBITE OF LAUGHTER)

GROSS: So it's just like so avant-garde. Do you know I mean? Like it's...

PERLMUTTER: No. What's odd about this whole game is that you have to get used to having your mind boggled left and right.

GROSS: Yeah.

PERLMUTTER: Right.

GROSS: Yeah.

(SOUNDBITE OF LAUGHTER)

PERLMUTTER: So, you know, even, you know, as soon as you just talk about a universe at all your mind boggles because, you know, you have to start asking questions like, you know, what's an infinite universe? And that's just mind-boggling. The picture then goes on and on with galaxy after galaxy forever, and then you say but what's the alternative? That would be even more mind-boggling; how could it not be like that? So you begin having your mind boggled and then you start throwing in extra ideas like, you know, light traveling through universe that is actually growing, where all the distances are getting bigger and, of course, it's just a bad place to start unless you enjoy having your mind boggled. And I sometimes think that the people who go into this field are the people who really love having your mind boggled a little bit at least once a day when they're working on something that seems very prosaic otherwise.

GROSS: Well, here's one thing that boggles my mind: If the universe is infinite then how can it be expanding because it's already infinite?

PERLMUTTER: Well, exactly. And I think the very term the Big Bang is getting in the way for most people here because whenever you hear the term Big Bang I think everybody immediately imagines that the universe is sort of this explosion of stuff out into empty space.

GROSS: Yes.

(SOUNDBITE OF LAUGHTER)

PERLMUTTER: But then the empty space is the universe, right, so that doesn't make any sense. So what I've been trying to trying out is there a different way of describing it and to see whether it helps. What I've been saying is just talk about today. Right at the moment as far as we know the universe could be infinite. It's likely to be infinite. And you have galaxy after galaxy after galaxy, as far as you want in any direction, and the only thing that's characteristic of it is that maybe there's an average distance between those galaxies. And when we say that the universe is expanding, all we really mean is that we're just pumping a little bit of extra space between all those galaxies.

So every distance is getting a little bit bigger. It's infinite now. It will be infinite, you know, in the future. There's an infinite number of galaxies now. There's infinite number of galaxies now. There's infinite number of galaxies in the future. The only difference is how dense is it, how crowded is the whole thing. Do you pump more space in between those galaxies? Or are they, you know, are they on top of each other?

GROSS: Wow. OK.

PERLMUTTER: So when you go backwards in time, you know, when you go backwards in time in a picture like that now you have, you know, a universe where you're sucking space out between galaxies, it's still infinite, and if you go far enough back they're all those galaxies are, you know, essentially on top of each other and all the stuff in the universe is essentially on top of each other, but it still could be infinite. And in some sense all we mean by Big Bang is going back far enough where things were so dense that we can't actually do the calculations anymore because our physics isn't, you know, doesn't really work well. That's not a very dramatic Big Bang. I mean I think we could call it like the big soup. But in some sense I think that is a better picture to have in your mind when we say in expanded universe than this incorrect idea of some stuff exploding into, you know, this space that can't be there.

GROSS: So sum up for us how you use the supernova to measure the rate of expansion of the universe.

PERLMUTTER: So putting this simple story together then, we use the brightness of the supernova to tell us how far away it is and hence, how far back in time that particular explosion occurred. We use its color and its spectrum to tell us how much the universe has stretched making the color of the supernova look redder since the time of that explosion. And then the only other thing we need to do is find a reasonable sample of supernova each with different brightness representing different times back in history so that we can make a little plot of how much has the universe stretched since, you know, eight billion years ago, seven billion years ago, five billion years ago, three billion years ago, and that's the plot on which we hope to see how much the universe was slowing down in its expansion.

GROSS: Saul Perlmutter shares this year's Nobel Prize in physics. He'll be back in the second half of the show. He heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory in the University of California at Berkeley. I'm Terry Gross and this is FRESH AIR.

(SOUNDBITE OF MUSIC)

GROSS: This is FRESH AIR. I'm Terry Gross, back with astrophysicist Saul Perlmutter. He shares this year's Nobel Prize in physics for the discovery that the universe is expanding at an accelerating rate. Perlmutter had expected to calculate the rate at which the expansion of the universe was slowing as a result of gravity. So this discovery of acceleration raises a lot of questions about existing theories of particles and forces. Calculating the rate of expansion of the universe required using the most powerful telescopes in the world to track supernova, ancient stars that exploded like five billion years ago, and measure their brightness, which you need to know to figure out the distance between stars at different points of time. Perlmutter heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory in the University of California at Berkeley.

Let's get back to supernova. So you're using the supernova, which are these exploding stars, stars that exploded billions of years ago, and you're studying their distance through analyzing the light that emanated from them. And you describe in something that you wrote, you say that supernova type 1-A, which is the type that you study, that they are a pain in the neck and to be avoided at all costs, that anything else would do.

(SOUNDBITE OF LAUGHTER)

PERLMUTTER: Yeah.

GROSS: In what sense are supernova a pain in the neck?

PERLMUTTER: Well, you know, they're wonderful for certain purposes. You know, the fact that they're so bright means you can see them, you know, across the vast distances of the universe and then that means you're getting to look way back in time, which is what we want to do because we want to see how much the universe has been slowing down. That's all great. But the problem is that they're, you know, in all other respects they're a real pain in the neck. They only explode a few times per millennium in any given galaxy and, you know, how long do you want to wait around to do your research project? They don't give you any advance warning at all when they're going to explode so, you know, what we need to do is we need to use the largest telescopes in the world. You have to apply for them months and months in advance and you might get one or two nights. And, you know, it makes a terrible proposal to say, you know, I would like to use the, you know, Tech Telescope on the night of March the 3rd because some time in the next, you know, few hundred years a supernova might explode.

(SOUNDBITE OF LAUGHTER)

PERLMUTTER: And, you know, of course, they...

GROSS: Out of all things.

PERLMUTTER: You know, and they don't last long. They disappear in a couple of weeks and you have to catch them on their way up. So that's the sense in which you, you know, when we started the project it seemed a little bit quixotic. So what we had to do is we had to figure out ways to turn what would otherwise be a, you know, a very, you know, awkward project into something that you could make very practical and reliable. And what it meant was essentially you had to come up with technologies, we developed some new cameras that would allow you to observe many, many galaxies all at one time on a very large telescope so that now you had a reasonably good shot that on a, you know, a couple of nights of observation there would be at least a few supernovas that would be exploding. And then we had to figure out some ways to time things so that, you know, we would guarantee that when we caught them we'd only catch the ones that were on their way up by comparing it to images that we'd just taken a few weeks earlier so it didn't give the supernova enough time to reach their peak and then start to fade.

And once we had figured out how to do that, which, you know, in retrospect, you know, it almost seems obvious, we then were able to start guaranteeing batches of supernova discoveries on a certain date. In fact, we could even time it with respect to, you know, being just before a new moon so that you could get these very faint objects observed while the night was - while the sky was dark.

GROSS: So let's define what we mean by the word telescope. Obviously it's not like your average stargazing telescope that you're using. Are you actually looking through a scope or is this like a computer that's scanning the skies and feeding you back information? Like tell us something about the telescope that you're using to find these five billion-year-old explosions.

PERLMUTTER: To find supernova, actually that's something that you can do. If you're looking for nearby supernova you can find them with a backyard telescope. In fact, when we began our work with the supernova the most prolific supernova discoverer was an amateur, Reverend Evans in Australia who used to just go out in his backyard every night and he remembered what some 200-300 galaxies looked like and he would just go from one to the other until he saw a speck of light that shouldn't be there and that was a supernova. So in that sense supernova are available to everybody and, you know, it's one of the nice areas where amateurs could really contribute to the field for many years.

But we needed to find supernova that were much, much more distant than these relatively nearby galaxies and so that meant we had to start using the very largest telescopes on Earth. These are telescopes that are, you know, typically oh, four meters across in their diameter of the glass, the mirror that you're collecting the lights with, and nobody, we've also lost that fun romantic image of looking through a telescope with your eye once we go to these large telescopes because when we began our work we were, astronomers were just converting from observing with photographic plates, where you would put a plate, a photographic plate and you would take these time lapse, you know, maybe 10 minute, 20 minutes exposures, to the new digital cameras. And that was one of the things that made a very big difference in us being able to do this project that the new CCD detectors had just become available, and we were just starting to use the first examples of them in astronomy. So it meant that actually the data would be - these images would be collected right on a digital chip that would read into your computer, an image. And then the problem became one of programming the computer to do the image analysis to be able to find these little specks of light that were the new supernova discoveries amid this, you know, this whole sea full of little distant galaxies in the images.

GROSS: Where does the telescope have to be in order to have a clear enough sky to see the distance it needs to see?

PERLMUTTER: These very large telescopes are sited at these beautiful remote mountain tops. So there's some wonderful telescopes that we used in Canary Islands. The U.S. has some at Kitt Peak outside Tucson. The ones that made the biggest difference for the discovery actually were the ones down in Chile because they're not only do you have a very dark clear sky where the atmosphere stays very still so the stars don't twinkle very much, but also the weather is very good for long periods on end during their summer time and that meant that you could actually follow objects that are rising and falling, like supernova.

In fact, the largest telescope on Earth that we needed at the time was the one that was designed here at Berkeley, in fact, the Keck Telescope on Mauna Kea in Hawaii. And there, you're taking advantage of these beautiful pristine skies at 14,000 feet. And so for long time one of the, I think one of the romantic elements of being an astronomer was that you would fly out to these distant spots. In our case we were always going out in a huge hurry and flying back in a huge hurry because we were trying to follow these rapidly, you know, disappearing supernova and so you would look at these gorgeous places and say boy, someday we should come back and visit.

(SOUNDBITE OF LAUGHTER)

GROSS: Right. If you're just joining us, my guest is Saul Perlmutter and he shares this year's Nobel Prize in science for the discovery of the accelerating expansion of the universe. And he heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory in the University of California at Berkeley.

Let's take a short break here, then we'll talk some more. This is FRESH AIR.

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GROSS: My guest is Saul Perlmutter and he shares this year's Nobel Prize in science for the discovery of the accelerating expansion of the universe. And he heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory in the University of California at Berkeley.

So you're making this discovery that the universe is expanding at an accelerating rate, meanwhile there's another team of scientists - two of whom you share this Nobel Prize with - who are finding similar results as you at the same time that you're finding them. Did you all know that you were working on the same thing?

PERLMUTTER: The supernova community is actually pretty small. It's international it, you know, includes people from all over the world, but you can fit almost everybody at a, you know, a supernova conference in a reasonably small lecture hall. So we all were constantly talking to each other and discussing what we were working on. And we were very aware when what had gone from a project that we were just trying to develop and trying to convince people that would work to a race with another team that was now using, you know, very similar technique to try to measure this expansion history of the universe. And so for the last, oh, you know, three, four years of the project we would be going down to these different telescopes in Chile and Hawaii and Tucson and you would often be back-to-back scheduled on your nights with the nights that the other team was on.

And, you know, some people would keep, you know, would try to be a little bit cagey with, you know, what they knew and what they didn't know at a given moment, but - and it was a pretty fiercely fought rivalry. But at the same time, we were the only people who understood each other's problems really, really well. And I, you know, there were at least a couple of occasions in which the other team had a really bad night where the weather was terrible and they weren't able to confirm any of the supernova they had discovered and, you know, that seemed so terrible that when we went on we took some observations for them. And then there was another occasion when our night, when we were trying to do our discoveries was clouded out at just the wrong time and the head of the other team, Brian Schmidt, exchanged nights with me so that we could stay on our cadence, our time cadence. So, you know, I think, you know, we were really out to, you know, to beat each other but, you know, we also knew that in some bigger sense we were all on the same team.

GROSS: In a way it's really lucky that both teams were working on this project simultaneously because you were able to corroborate each other's findings. Like if you found information that contradicted common thinking then you conceivably could've been written off as being inconsistent with what everybody else believed. But when two teams found the same thing, well, then you kind of have to believe it, right?

PERLMUTTER: Absolutely. I mean the first, oh, the first meetings in which the results were being presented, you would ask, you know, some leading cosmologist in the room and they would say there's got to be something wrong, this can't be right. And everybody knew though that both teams were in a, you know, pretty fierce rivalry and that either one would be happy to show what was wrong with the other one's result and yet both teams agreed. So oh, I would say about three months later that a large meeting was held with cosmologists from all over and the two teams were being grilled about the results and by the end of that meeting when they asked for a show hands most people in the room had said they were now starting to accept the results. And I think that would not have happened if it weren't for two teams representing such, you know, diverse range of this community able to corroborate each other.

GROSS: You know, what I find so funny? Like you're getting the Nobel for this like incredibly advanced...

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GROSS: ...study in cosmology and the Nobel committee couldn't reach you to tell you you'd want the Nobel because they had the wrong phone number.

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GROSS: So you found out from journalists who were calling you. And it's just so funny that something so kind of practical and small like your phone number like they didn't have that right.

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PERLMUTTER: No, in fact, it was for a nice reason in some sense because, oh, one of my collaborators on the project, Ariel Goobar in Stockholm, knew me for so long that when they called him up he was flustered and he looked in his cell phone and he forgot that he had actually had an old cell phone number as well as a new cell phone number for me. So he, you know he gave the wrong number. Somewhere in Berkeley my, the wrong number was ringing for 45 minutes. You know, somebody could have answered the phone and won the Nobel Prize.

GROSS: Somebody who failed science would've gotten this call.

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PERLMUTTER: In fact...

GROSS: Congratulations. You won the Nobel.

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GROSS: So when the journalists called you did you believe them?

PERLMUTTER: Well, fortunately my wife, you know, who woke up in the bed next to me reached over and grabbed her iPad and by, you know, halfway through the conversation with the first reporter she was already pointing to the screen saying look it's, you know, you have won.

GROSS: Amazing. Now correct me if I'm wrong, the conclusion that you reached about the accelerating expansion of the universe, you reached that conclusion in 1998 and you win the Nobel this year, 2011. What accounts for the distance between the discovery and the prize?

PERLMUTTER: The Nobel prizes have always kept a element of mystery about exactly how the selection works, so we always are doing, you know, tea leaf reading to try to figure out what's really going on in that decision. But my understanding is that they really want to make sure that a result is completely established. And they don't want to give a Nobel Prize and then a few years later for something to overturn that result. So in this particular case I think people thought this might actually been a rather fast Nobel Prize because people had accepted this result so quickly and because there have been now other techniques used to make measurements that corroborate this without supernova.

So I think today if there were no supernova in the story, if there was no supernova measurement we would probably still believe the basic conclusion that we found using these other measurement techniques.

GROSS: Now your father is a professor emeritus of chemical and biomechanical engineering at the University of Pennsylvania. When you were young did he get you excited about science?

PERLMUTTER: I think I grew up in a family that was full of lots of discussions of all sorts of things. And my father was the person who I could talk science with, because, you know, he's a professor in chemical engineering. My mother is actually a professor, as well, in social work. And so - and they were very social people who would always have lots of friends and colleagues over. And I think I've always enjoyed learning about all aspects of the world.

And I think, in some sense, that stood me in as good stead as specifically the science part, because I think I've always wanted to know more about how the world works in many respects, you know, in terms of - with people and with physics. And so I think that that combination makes a very big difference. In some sense, doing science of this particular kind is such a social activity, that growing up in a very social environment is, I think, almost as important as growing up in a scientific environment.

People sometimes think of science as if it were the lone scientist disappearing into the laboratory and, you know, with their white coat and coming up with the eureka moment. But my experience of science is almost the opposite, that it's perhaps the most social thing you can do. You're working with people all the time. And the best ideas are the ideas you're coming up with in groups of researchers that are getting together every week, in the larger groups that meet at meetings, you know, every few months. And I think it's that social aspect that people often forget about.

GROSS: So as prestigious as it is to win a Nobel, apparently one of the things that really matters to you is that with a Nobel at the University of California at Berkeley, you get a free parking spot. And apparently, parking spots are really hard to find. So have you started using that free parking spot yet? Or do you have to wait until after the award is officially presented in Sweden?

PERLMUTTER: No. They always put up the new parking spot sign. So it's now in a line of parking spots for Nobel laureates. Berkeley is very productive in this respect. And I will say that, you know, growing up as a, you know, kid in an urban environment and having lived in cities all my life, you know, of course the one achievement that you could - that everybody could look forward to would be getting the perfect parking spot.

And I will say that even at my wedding, you know, a number of years ago, one of my oldest friends had in his particular toast to me pointed out that my - you know, I was known for being able to find parking spots in cities. So I think is an extra element for me of this parking spot in a university campus.

GROSS: So apparently what he said was prophetic.

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GROSS: Through studying the supernova, you could find the perfect parking spot.

PERLMUTTER: It's remarkable what you can find when you look out into distant space.

GROSS: Exactly. So am I right in thinking that you helped date how old the universe is, that your work helped date that?

PERLMUTTER: Yes. We describe the age of the universe back to the time at which it was so dense that we aren't able to go any further back yet in our understanding of, you know, how everything began. So we call that the beginning of the universe. But, of course - and we measure it by using this expansion history of the universe. So if the universe was expanding at a constant rate, you would get one date when you look back in time.

But the fact that we are seeing that the universe was slowing down for the first half and then accelerating for the last half, that ends up giving you a different date for the - how old it is back to that date where we (technical difficulties) . So we call that (technical difficulties), and we say that it's about 13.7 billion years now that we estimate that we can go back.

GROSS: (Technical difficulties) as the universe? And how...

PERLMUTTER: Billion.

GROSS: Billion. Yes. And how old are you?

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PERLMUTTER: So I just turned 52.

GROSS: Which seems, by comparison, a really short amount of time. You know, I - go ahead.

PERLMUTTER: I was going to say, sometimes people, you know, ask, do you find it frightening to imagine living in such a vast space and be talking about such vast times? And I've even say that I feel somehow we seem to be very lucky to have been born in this nice, in-between scale, where we're just big enough to study these vast spaces that are larger than us, and also the tiny, microscopic spaces of, you know, the atoms that we're made out of.

And we're also - are - you know, of an age where we can - where we're just old enough to be able to ask questions about things that are billions of years older, and also things that are, you know, microseconds or nanoseconds shorter than our lifetimes. And so, in some sense, we're in a sort of comfortable, cozy middle, if you can call that cozy.

GROSS: Saul Perlmutter, congratulations again on the Nobel. Have a good trip to Sweden. And thank you so much for talking with us on FRESH AIR.

PERLMUTTER: Oh, thank you. It's been a pleasure.

GROSS: Saul Perlmutter shares this year's Nobel Prize in physics. He'll receive the prize at a ceremony in Stockholm December 8th. Perlmutter heads the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory and the University of California at Berkeley. He's a professor at the university.

Coming up, Kevin Whitehead reviews new albums that mix jazz with Argentine and Brazilian music. This is FRESH AIR. Transcript provided by NPR, Copyright National Public Radio.

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